Effects of Taking Daily Antihistamines

Antihistamines can be an indispensable tool in dealing with the symptoms of seasonal allergies. They are widely used by both children and adults to combat itchiness, stuffy nose, watery eyes, hives, and other symptoms linked to allergens such as pollen, dust mites, ragweed, pet dander, certain foods, and other potentially irritating substances. But what are the potential side effects of long-term, daily use?

Typical Side Effects

The typical side effects of antihistamines, as disclosed on their packaging includes symptoms such as drowsiness, dry mouth, dizziness, nausea, vomiting, restlessness or moodiness in children, blurred vision, confusion, or even trouble urinating. Not everyone will experience these side effects, and not all medications in the antihistamine group cause all of them, but anyone may experience any of them at any time while taking certain antihistamines. Drowsiness is the most common side effect, especially with older, “first generation” formulas of antihistamines such as those used in Benadryl, Tavist, and Chlor-Trimeton. Newer drugs like Allegra, Zyrtec, and Clarinex may cause fewer day to day side effects, though the long-term side effects of daily antihistamine use is still largely unknown.

What We Know

On top of the usual side effects applicable to occasional use, there may well be additional effects when antihistamines are used daily or almost daily over a prolonged period of time. While the research is still being done on this topic, there is enough evidence so far to warrant caution and moderation on the part of frequent antihistamine users, less they end up with side effects that are worse and more debilitating than their initial allergy symptoms. Some people report off-label usage with dosage of at least double the recommended amount for the long-term treatment of chronic hives or other conditions with no adverse side effects. Others report that, over time, antihistamines can become less and less effective at treated their symptoms. Sometimes this problem can be fixed by switching to a different formulation of antihistamine, but sometimes not.

Abuse of Antihistamines

Abuse of antihistamines for recreational purposes or other off-label usage can be harmful both in the short term and the long term. Diphenhydramine, which is the main active ingredient in many antihistamines, including Benadryl, affects the central nervous system, producing wide and varied side effects in different people. Possible side effects from short-term usage may include light-headedness, loss of coordination, dry nose, throat, and mouth, blurred vision, gastrointestinal upset like nausea, vomiting, constipation, diarrhea, or urinary retention, spatial and mental disorientation, drowsiness, loss of appetite, temporary erectile dysfunction in men, visual and aural distortions, muscle relaxation, nervousness, insomnia, mild to moderate hallucinatory experiences, and, strangely, an increased appreciation of music. Long-term or high dosage use of antihistamines may cause seizures, arrhythmias or heart palpitations, loss of consciousness, hypotension, and even cardiac arrest. Overdose is possible on antihistamines, and can be fatal. Symptoms of an antihistamine overdose include drowsiness, dilated pupils, flushed, dry skin, fever, delirium, convulsions, and hyperthermia.